Pulse generator



PULSE GENERATOR original Filed Dec. so', 1944 l JB i C HD E fL//C Y lELAY /NVE/vro/z TTY Patented Oct. 18, 1949 n PULSE GENERATOR.

Hilmar` C. .Lindahl, Waltham, Mass., assignor to Raytheon Manufacturing Company, Newton, Mass., a corporation of Delaware GriglinalY application December 30, 1944, Serial No. 570,671. Divided and this',applicationJan-V uary 19, 1946, Serial No. 642,401

(Cl. Z50-36) 1 Claim.

"This is a division o'my copending application, Serial No. 570,671, led December 1944.

This invention relates to electrical systems and more 'particularly Ato pulse-forming circuits suitable, for example, for generating and shaping pulsesv oi'current having duration and repetition frequencies ofthe order required for --the energization of a magnetron in radar equipment.

'It is amongthe objects of the invention to provide a 'pulse-forming circuit the characteristics of which 'may be varied Within wide limits at the Wil'lof'the operator for the purpose of altering the repetition frequencies ofthe pulses generated by the system.

A' further obJ'eCtOf the invention is to provide a circuit ofthe type described in which the duration of the pulses generated can be controlled within wide limits.

A further object of the invention resides in the provision of a pulsefforming circuit in which adjustments for lvarying the repetition kfrequencies and for altering the pulse Width or duration maybe easily madeby inexperiencedoperators.

A further object of the invention resides in the provision of a circuit of the type described which may bey easily constructed of readily available materials and whichwill be suiciently ilexible to render it suitable for use under the varying conditions required by a magnetron test bench.

The above and other objects and features of the invention Willlbe made fully. apparent to those skilled in theart from a consideration of the iollowing detailed'descript'ion taken in conjunction with the accompanying drawing yin which.:

Fig. 1 shows a circuit diagram illustrating an embodiment ofthe invention; and

Fig. 2 .showsa set of curves illustrating qualitatively rather than Iquantitatively the nature of the pulse generated at .various points in the system.

Referring to the drawing, and especially Fig. l, the system illustrated :comprises a tube I which may be of the type designed for use in the output stage of radio receivers, such as a 6V6, and having a plate 2, an indirectly heated cathode 3, a grid 4 and a screen-5.11 Apotentialnof about v300 volts is applied to the plate 2 fromva supply line I5'r is grounded sistor III-prevents the'tube I from being` driven tooV 'hard 4and also serves to prolong l"the period' duringwhich the tube I is conductive, rthereby obtaining a `pulse duration of approximately ythe desired length. After a predetermined timeyin' this instance about ve microseconds, the charge on the condenser I -I becomes 'so high that the tube:v

l is blocked, lterminating the pulse of current;

The charge on the lcondenser I-I leaks oli'throughthe variable resistor I3.' The period'of'time required to leak offthis charge dependsY on thev value of the resistor I3, which valuemay'be selected by the operator. Thus, the-'period'oftime before the start of the next ypulse-may be-varie'd,

and 4accordingly the repetition rate of the system, may be controlled. The duration of the pulse of' initial design and manufacture of thetransformer.

to give the pulses the desired duration yin a given circuit, I prefer to provide a means for controlling, within limits, the characteristics of the transformer. To-this end the transformer't is provided with a third winding I4,"the ends of,

which .are connected'through a variable resistor I5 and a condenser Iii,r Variation of the resist'- ance i 5 `alters the pulse width. This variation'also alters the repetition rate since it affects thef'feed back. Accordingly, in practice, the resistor I5is first set to adjustthe Width of the pulse through .the tube I to the desired duration and thereafter resistor I3 may be adjusted to give the desired repetition rate.

The fourth winding II of the transformer 8 applies the positive pulse through the tube I, illustrated by the curve Bof Fig. 2, between the grid I8 and the cathode 20'of a tube 2I throughv a coupling` condenser I9. Tube 2JI, of the vsame type as tube I, has its plate 22 connected to the supply line 6. The screengrid123` oitube 2'I is also connectedk to the supply line E through a voltage dropping, resistor 24Vand isalso connected tothe cathode 2l) through a coupling condenser 25. Biasing resistors ZGand .26 areconnected between the grid .I'I' and ground and `between cathode 2t!V and ground, respectively. The condenser IS7-is so large that its charge will not change appreciably during the duration of the pulse B applied vbetween the grid I8=and=the cathode 2D. An amplified positive pulsefof around 200 volts, illustrated by the curve C of Fig. 2, is obtained between the cathode 2D of the tube 2I and ground. Condenser 25 applies this pulse to the screen 23 so that tube 2I operates as a tetrode even though performing the functions of a cathode loaded am pliier.

The pulse C is also applied to a delay line 21 connected to the cathode through a coupling condenser 28. The opposite end of the delay line 21 is connected to ground through a resistor 29 which absorbs energy from the pulse and reduces the reflections produced by the pulse after passing through the delay line 21. The amount of the delay imposed upon the pulse by the delay line 21 can be selected by a switch 30 which may be closed at various points P1, P2 and P3 along the delay line. The presence of phase distortion will give the delayed pulse a small negative component at the beginning thereof, as seen at the lefthand end of the curve D, and will also cause a small ripple in the top of the pulse, but these are of no consequence, provided they are not of eX- treme magnitude. The delayed pulse is applied to the grid 32 of a tube 3| through a resistor 33. The resistor 33 smooths out the irregularities in the pulse D, which are' due to reflections. The

tube 3| is of the same type as tubes |y and 2| having a cathode 311 connected to ground through a biasing resistor 35 and a by-pass condenser 36. The cathode 34 is also connected to the supply line 6 through a voltage dropping resistor 31. The plate 38 of the tube 3| is connected to the supply line 6 through a Voltage dropping resistor 39. The plate 38 is also connected to the output line through a coupling condenser 4|. A screen 42 of the tube 3| is directly connected to the supply line 6.

A negative pulse is obtained from the plate of the tube 3| delayed behind the pulse at the cathode of tube 2| by the amount of delay caused by the delay line 21. The undelayed pulse C at the cathode 29 of the tube 2| is applied to the output line 40 through the resistor 43. The delayed negative pulse on the plate 38 of the tube 3| combining with the positive pulse at the cathode 2U of the tube 2| cuts off or counteracts the right-hand end of the wave C to make this pulse shorter, as shown in the curve E of Fig. 2. The initial portion of this curve, together with the dotted line curve C', correspond to the undelayed pulse C. The solid line curve E is the resultant of the curves C and D combined. When the switch 30 is in the last position P4 to the right, the control grid 32 of the tube 3| is grounded, making this tube inoperative. In this case the full pulse C would be available at the output. As the switch is m'oved farther to the left to the point P3, the clipping action of the pulse D is imposed upon the pulse C toward the end thereof and a shorter pulse is obtained. As the delay period is shortened by moving the switch to the points P2 and 'r' P1, the delay becomes less and less and the resultant length of the pulse E available at the output becomes shorter and shorter.

The output of the pulse-forming circuit shown may be utilized for various purposes where a pulse which is closely controllable with respect to both duration and repetition frequencies is desired. For example, the pulse may be applied by way of a concentric cable to the grid of a pulse amplifier, and the amplified pulse used to energize a magnetron in radar equipment, and is particularly suitable for the purpose of testing such magnetrons. When used for the latter purpose, it is advantageous to also derive a small voltage pulse simultaneouslyrwith the output voltage at 40 t0 operate the slave sweep circuit of a synchroscope. To this end a small negative voltage pulse indcated by curve A of Fig. 2 may be taken from' the plate of the tube 1 by Way of a coupling condenser 34 and a concentric cable 45.

From the foregoing it will be seen that the invention provides a pulse system in Which both the repetition frequency and the duration of the pulse may be varied through wide limits by adjusting the value of resistance I3 and by adjusting the delay line 21, respectively. The value of the resistor |3 is preferably variable continuously or by small graduations from five megohms down to a low value. The delay line 21 should be comparatively fiat to obtain even retardation along the length thereof. For this purpose I have successfully used a coil about 131/2 inches long on a one-inch libre rod with 5% X .0025 nickel strips running longitudinally thereof and grounded as indicated at 46. This is covered with one layer of three mil polystyrene over which is Wound evenly No. 34 enamel Wire to fill the rod.

While the invention has been described in conjunction With one embodiment thereof, other embodiments within the scope of the appended claim will be apparent to those skilled in the art from' a consideration of the form shown and the teachings hereof. n

Accordingly, a broad interpretation of the appended claim commensurate with the state of the art is desired.

What is claimed is:

A pulse generator including a transformer, a therrnionic tube having its anodeconnected to a source of positive potential through a Winding of said transformer and its control grid connected to a second winding of said transformer, a condenser in the connections between said transformer and said control grid, a resistor between said control grid and said condenser whereby a iow of current through said tube and said rst winding induces a current in said second winding to establish a blocking potential on said grid after said condenser becomes charged to a predetermined value, a leak circuit connected across said condenser and including a variable resistor for controlling the frequency of the pulse of current through said tube by controlling the time required for the discharge of said condenser, a third Winding on saidtransformer, and a circuit including a Variable reactance coupled to said transformer for altering the characteristics of said transformer to control the duration of the pulse of current through said tube.

HILMER C. LINDAI-IL.

REFERENCES CITED The following references are ofrecord in the le of this patent:

UNITED STATES PATENTS Kessler Sept. 18, 1945 

